1. Field of the Invention
The present invention relates to an optical recording and reading method for an optical recording medium including a plurality of recording and reading layers and to the optical recording medium.
2. Description of the Related Art
Conventionally, optical recording media such as CD-DAs, CD-ROMs, CD-Rs, CD-RWs, DVD-ROMs, DVD-Rs, DVD+/−RWs, DVD-RAMs, Blu-ray Discs (BD) are widely used to view digital video contents and to record digital data. In the BD standard, which is one of the next generation DVD standards, the wavelength of the laser beam used for recording and reading is reduced to 405 nm, and the numerical aperture of an objective lens is set to 0.85. In optical recording media conforming to the BD standard, tracks are formed at 0.32 μm pitch. This enables 25 GB or more data to be recorded on and read from one recording and reading layer of such an optical recording medium.
It is expected that the size of video and data files will increase more and more in the future. Therefore, it is contemplated to increase the capacities of optical recording media by using a multiple stack of recording and reading layers. In the technologies for BD standard optical recording media reported by I. Ichimura et al., Appl. Opt., 45, 1974-1803 (2006) and K. Mishima et al., Proc. of SPIE, 6282, 62820I (2006)6 to 8 recording and reading layers are provided to achieve ultra large capacities as much as 200 GB.
When a multiple stack of recording and reading layers is used in an optical recording medium, projections and depressions, such as grooves and lands, for tracking control are formed on each recording and reading layer, and therefore a stamper (a master die) must be used to form the projections and depressions each time a recording and reading layer is formed. Therefore, as the number of stacked layers increases, the number of times the stamper is used increases, and this may result in an increase in manufacturing cost.
In the technologies for optical recording media recently proposed in Japanese Patent Application Laid-Open Nos. 2008-97693, 2008-97694, and 2008-108383, servo layers are provided separately from recording and reading layers, and information is recorded on each recording and reading layer using a recording laser beam while a tracking signal is obtained from a corresponding one of the servo layers using a servo laser beam. With such technologies, the recording and reading layers need not have projections and depressions (grooves) for tracking information, and a stamper need not be used for the recording and reading layers during manufacturing. This enables a significant reduction in cost.
In the optical recording media described in Japanese Patent Application Laid-Open Nos. 2008-97693, 2008-97694, and 2008-108383, content information and other information, in addition to address information, are added to the data recorded on the recording and reading layers so that the recorded data can be read using only recording marks formed on the recording and reading layers.
However, in this case all the recording and reading layers must be consulted to check the contents recorded on each recording and reading layer. Therefore, when the number of recording and reading layers is increased, there is the problem in that seek operation before reading takes a considerable amount of time.
Another problem is that, to perform recording, all the recording and reading layers must be consulted to identify which addresses in which recording and reading layer can be used for recording, and therefore preparation for recording takes a considerable amount of time.